Environmental Analyses by TXRF - NEXAFS and IR-SpectroscopySpeciation of Bromine in Organics and Characterization of the Organic Matrix

B. Beckhoff1, O. Hahn2, J. Weser1, M. Wilke3, G. Ulm1, O. Jann2

1Physikalisch-Technische Bundesanstalt (PTB)2Bundesanstalt für Materialforschung und –prüfung (BAM)

3Universität Potsdam, Institut für Geowissenschaften

• motivation

• emission measurements of PBFR

• synchrotron based infrared spectroscopy

• TXRF

• TXRF – NEXAFS

• conclusions

outlineEmission from

Materials

• flame retardants (FR) have been used in polymers since the 1960s

• special attention has been given to brominated FR concerning their toxicity and eco-toxicity

• environmental analyses indicatetheir presence in a wide range of different samples

• the aim of former studies was to analyse the emission of certain FRs from selected products to determine their contribution to the contamination of the indoor /outdoor environment

• the aim of this present study is the analysis of trace constituents (e.g. polybrominated FR in polymer matrices) in “artificial” fine dusts

motivationEmission from

Materials

• polybrominated biphenyls (PBB)

• polybrominated diphenylether (PBDE)

• tetrabromo-bisphenol A (TBBPA)

• hexabromocyclododecane (HBCD)

Most of them belong to semi volatile organic compounds (SVOC)⇒ Boiling points > 300 °C⇒ special requirements for sample preparation and analysis method!

polybrominated flame retardantsEmission from

Materials

Br

Bry

x

O

CH3

CH3

OHOH

Br

Br

Br

Br

Br

Br

Br

Br

B r

Br

Br

Bry

x

aliphatic

aromatic

Interesting distinctionbetween compoundsdue to the fact thatsome aromatic PBFRsare forbidden!

printed circuit board under working conditions

0 20 40 60 80 100

1

10

100

1000

10000heated (60 °C)non-heated (23 °C)

organophosphate FR brominated FR brominated FR

Con

cent

ratio

n, n

g m

-3

Test time, days

emission test measurementsEmission from

Materials

• sampling on polyurethane foams (PUF)• foams were extracted with suitable solvents• qualification/quantification with GC-MS

0.02 m3-emissiontest chamber

0.001 m3-emissiontest cell very low emission rates!very low emission rates!

analyses of „dust“ samples on wafersEmission from

Materials

Distribution of PBFR in the environment• caused by emission into air?• due to fine dust transfer into environment?

In order to simulate prospective experiments based on cascade impactorsfor sample collecting, some polymers containing brominated flame retardants were put onto an ultra-pure silicon wafer surface

polystyrene(PS) with

HBCD

polystyrene(PS) with

HBCD

polystyrene(PS) withTBBPA

polystyrene(PS) withTBBPA

copolymerwith

TBBPA

copolymerwith

TBBPA“model-system“

Schade et al., New infrared spectroscopic beamline at BESSY II, Rev. Sci. Instruments, Vol. 73, No. 3, 1568 (2002)

F1: diamond window: seperation UHV / forevacuum

M2/M3: cylindrical mirror

M1: plane mirror

organic analyses using synchrotron IR Emission from

Materials

• SR-IR light is 1000 times brighter than conventional IR sources• SR-IR light is highly collimated like a laser• SR-IR light emits a wide range of infrared wavelengths• making Fourier Transform IR spectroscopy possible (Michelson Interferometer)

⇒ non - destructive measurements in reflection⇒ high lateral resolution⇒ analyses of organic matter

organic analyses using synchrotron IR Emission from

Materials

organic analyses using synchrotron IR Emission from

Materials

3500 3000 2500 2000 1500 1000

-1,0

-0,5

0,0

0,5

1,0

1,5

Sample, raw data Sample, norm.

Abs

orpt

ion

(nor

m.)

Wavenumber, ν/cm-1

• furthermore: background correction necessary!

• gold sputterd wafer as reference for reflection measurements

• structure is caused by an interaction between thin layeron wafer and infrared light

• interference phenomena

organic analyses using synchrotron IR Emission from

Materials

3500 3000 2500 2000 1500 10000,0

0,2

0,4

0,6

0,8

1,0

Sample Polystyrene

Abs

orpt

ion

(nor

m.)

Wavenumber, ν/cm-1

• Identification of polymer(e.g. PS) is possible

• no indication of existenceof (0,5 – 3 %) PBFR

Another technique for trace element / component is necessary!

Total-reflection X-Ray Fluorescence (TXRF) analysis:demands for ultra-trace analysis and advantages PBI I

X-Ray Spectrometry

particular advantages of TXRF :

- low scattering background contributions

due to small penetration depth ( a few nm )

- large solid angle of detection

- absolute detection limits in the fg/pg range

Energy dispersive detector Fluorescence

radiation

reflected beam

incidence beam

φ < φcrit

IoIfenergy-

dispersivedetectorincident radiation

fluorescenceradiation

reflectedradiation

Demands for ultra-trace analysison silicon wafer surfaces:

For Al, Ti, Zn detection limits of 2•109 atoms/cm2 are required.

For Ni, Fe, Cu and Na detection limits of 3•108 atoms/cm2 are required.

SR-TXRF facility for 200 mm and 300 mm silicon wafers

Picture of the entire arrangement, including

the cleanroom, the high-vacuum load-

lock, the UHV (T)XRF analysis chamber and

a conventional Si(Li) detector.

PBI I

X-Ray Spectrometry

PBI I

X-Ray Spectrometry

TXRF analyses of brominated compounds

CO

Br

• characterisationof Br is evident

• what about a chemicalspeciation of Br?

total reflection X-ray fluorescence

analysis

Fine structure of theX-ray absorption

in near-edge regions(fluorescence detection)

PBI I

Varying the excitation energy, the fine structure of the X-ray absorption can beprobed in near-edge regions (NEXAFS) in order to distinguish different compounds.

speciation of bromine

No change in the TXRF arrangement is needed, but the tunability of the incident photon energy and a sufficient energy resolution are required.

X-Ray Spectrometry

Near-edge X-ray absorption fine structure: transmittanceversus Total-reflection X-Ray Fluorescence (TXRF)

particular advantages of TXRF :- low scattering background due tosmall penetration depth

- large solid angle of detection- absolute detection limits in the fg / pg range

If ∼ μ as μ≈τ for soft x-raysμ = −ln (It /I0) /d

general requirements:- high-energy resolution- high photon flux for dynamics- high spectral purity

Ioincidentradiation

transmittedradiation

It

d

μ

transmittance fluorescence detection

Energy dispersive detector Fluorescence

radiation

reflected beam

incidence beam

φ < φcrit

IoIfenergy-

dispersivedetectorincident radiation

fluorescenceradiation

reflectedradiation

PBI I

X-Ray Spectrometry

Near-edge X-ray absorption fine structuresrecorded in transmission measurements

The near edge x-ray absorption fine structure(NEXAFS) arises from electronic transitions of aninner shell electron to energy levels (orbitals inmolecules, bands in solids) which are normallyunoccupied in the ground state. The lowestunoccupied molecular orbital (LUMO) is the π* orbital in essentially all unsaturated compounds.

absorption

photonenergy

C 1s NEXAFS spectra of some common polymersas recorded in transmission experiments.

http://unicorn.mcmaster.ca/research/stxm-intro/polySTXMintro-all.html

PBI I

X-Ray Spectrometry

chemical speciation at the K-edge

13610 13620 13630 13640 136500,0

0,2

0,4

0,6

0,8

1,0

HBCD (aliphatic) HBB (aromatic)

norm

. Br-

Ka

CR

photon energy / eV

G. Falkenberg et al.: Comparison of conventional and total reflection excitationgeometry for fluorescence X-rayabsorption spectroscopy on droplet samples

carbon atom with sp2

hybridisation is more electrophilic (smaller shielding of ligand in NMR-experiments)

electron density of bromine which is bonded to an aromatic carbon is reduced

binding energy of the electron which has to be excited in other energy level is increased

Chemical shift of Br-K-edge iscaused by different hybridisationof carbon (sp2 and sp3)

PBI I

X-Ray Spectrometry

chemical speciation at the L-edge

1545 1550 1555 1560

0,0

0,2

0,4

0,6

0,8

1,0

HBCD (aliphatic) TBBPA (aromatic)

norm

. Br-

La C

R /

(nW

s)-1

photon energy / eV

• effect is also visible in the region of theBr-L-edges

• due to the electronic structurechemical shift is less characteristic

1547 1554 1561

0,0

0,2

0,4

0,6

0,8

1,0

1,2

HBCD TBBPA copolymer with TBBPA polystyrene with HBCD

norm

. Br-

La C

R /

(nW

s)-1

photon energy / eV

• effect is again visible in original samples containing PBFR!

• influence of matrix on fine structure due to adsorption effects?

PBI I

X-Ray Spectrometry

influence of matrix on fine structure

• further measurements (e.g. HBCD in different polymer matrices) are necessaryfor convincing absorption corrections

1547 1554 1561 1568 1575 1582 1589

0,0

0,2

0,4

0,6

0,8

1,0

HBCD PS with HBCD

norm

. Br-

La C

R /

(nW

s)-1

photon energy / eV

Conclusions – prospective fine dust analysesEmission from

Materials

• first results demonstrate some potential of the TXRF-NEXAFS method to contribute to the elemental speciation, even of trace elements

• distinction between bromine which is bonded to an aromatic carbonfrom another bromine which is bonded to an aliphatic system is possible

• the shape of the various TXRF-NEXAFS structures reflects the influence of the chemical environment on the element bromine

• further investigation are necessary to analyse the influence of different polymer matrices (aliphatic such as PE or aromatic such as PS) on the TXRF-NEXAFS structures

• synchrotron based FTIR spectroscopy in reflection mode will provide the classification of different polymers within reasonable measurement times

• difficult to characterise trace components in polymer matrices

acknowledgementsEmission from

Materials

Gerald Falkenberg (HASYLAB)

Ulrich Schade (BESSY)

Timo Wolff (TUB / BAM)

Thank you for your attention!